1. Field of the Invention
This invention relates to a recording medium and a substrate for a recording medium to be used in a recording and reproducing device which performs recording and reproduction by use of a scanning probe, wherein reproducibility of recording and reproduction of information is improved. The invention also relates to a method for preparation of the recording medium.
Also, the present invention relates to a recording, reproducing and erasing method and a recording and reproducing device which performs recording and reproduction with good reproducibility by use of such a recording medium.
2. Related Background Art
In recent years, the use of memory materials has formed the nucleus of electronics industries, such as computers and their related instruments, video discs, digital audio discs, etc., and development of those materials also has been under active progress. The performance characteristics demanded for memory materials may differ depending on uses, but may generally include:
(1) high density and large recording capacity; PA1 (2) rapid response speed of recording and reproduction; PA1 (3) small power consumption; and PA1 (4) high productivity and low cost; etc.
Heretofore, semiconductor memories or magnetic memories employing magnetic material or semiconductor material as the base material have been predominant, but with the advancement of laser technique, inexpensive and high density recording media with optical memory using an organic thin film such as an organic dye, photopolymer, etc. are now emerging in the field of art.
On the other hand, recently, a scanning type tunnel microscope (hereinafter abbreviated as STM) capable of observing directly the electron structure of the surface atoms of a conductor has been developed [G. Binnig et al, Helvetica Physica Acta, 55, 726 (1982)], and it has become possible to measure both single crystalline and amorphous materials with high resolving power of real space image. In addition, this method has the advantage that observation can be made at low power without caused damage by current to the medium. Further, it can be operated in an air environment and applied to various materials, and therefore a broad scope of applications are expected.
STM is based on the phenomenon that tunnel current flows when a probe and an electroconductive substance approach each other at a distance of about 1 nm with a voltage applied therebetween. This current is very sensitive to the distance change between them, and by scanning the probe so that the tunnel current is maintained constant, the surface structure of the real space can be drawn and at the same time a variety of information about the total electron cloud of surface atoms can be read.
In this case, resolving power in the interplanar direction is about 1 .ANG.. Therefore, by applying the principles of STM, it is possible to perform high density recording and reproduction sufficiently in the order of an interatomic distance (several .ANG.). As a recording and reproducing method in this case, there has been proposed a method in which recording is performed by changing the surface state of an appropriate recording layer by use of a particle ray (electron beam, ion beam) or a high energy electromagnetic wave such as an X-ray or an energy ray such as visible light or UV-ray, etc., and reproduction is effected by STM, and a method in which a material having a memory effect for switching characteristics of voltage and current, for example, a .pi.-electron type organic compound or a chalcogenide thin film, is used as the recording layer, and recording and reproduction are performed by use of STM, etc. (Japanese Patent Laid-Open No. 63-204531, No. 63-161552, No. 63-161553).
Also, in recent years, based on such STM technique as mentioned above, there has been invented a method for measuring various mutual interactions between a probe and a test sample. Also by utilizing such a scanning probe, high density recording and reproduction can be performed. For example, by use of an intramolecular force microscope (hereinafter abbreviated as AFM) which measures the intramolecular force acting between a probe and a test sample, even if the recording medium is completely insulated, its surface shape can be detected on an atomic order.
In such a recording and reproducing method as described above, in order to practically record and reproduce a large amount of information, it becomes necessary to perform positional detection and correction control (tracking) of a probe in the XY direction (interplanar direction of recording medium).